Question: If $x \bigtriangledown y = xy+3x-y$ and $x \bigtriangleup y = 7x-3y$, find $(-2 \bigtriangleup -4) \bigtriangledown -5$.
Explanation: First, find $-2 \bigtriangleup -4$ $ -2 \bigtriangleup -4 = (7)(-2)-(3)(-4)$ $ \hphantom{-2 \bigtriangleup -4} = -2$ Now, find $-2 \bigtriangledown -5$ $ -2 \bigtriangledown -5 = (-2)(-5)+(3)(-2)-(-5)$ $ \hphantom{-2 \bigtriangledown -5} = 9$.